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66 Supro THUNDERBOLT 6420 Amp Black Tolex ALL Original US made
This is one of the RARE 1966 Supro Thunderbolt amps in Black tolex. This amplifier has a legendary status among guitarists worldwide. Driven much by the Jimmy Page connection and mystery surrounding the means to achieve the tone captured on the first two Led Zepplin albums. Jimi Hendrix was also known to us the Supro Thunderbolt amp from this time period. These great amps were made by the Chicago based contact manufacturing house Valco. Valco also made other consumer electronics goods along with their offering of instrument amplifiers. Valco made their own line of amplifiers as well as private labeled offerings for Wards/Airline, Gretsch, National, Oahu, Harmony, Penncrest and Supro.
Introduced in late 1964, the Thunderbolt was intended as a bass amplifier for the Jazz player. As such, it was not a good design. The baffleboard was thin and allowed too much speaker movement softening the sound. The tube rectified model also suffered power supply sage which contributed to a lack of punch. As the music of the day was moving toward a more percussive bass sound, the Thunderbolt was panned by bass players. The Thunderbolt featured a simplistic two knob control layout, (one volume and one tone) two 12AX7'S and a pair of 6L6 output tubes. The 1964 and 1965 models were covered in the gray colored "Rhino Hide" materal shown on the example to the right. This covering was listed as "Midnight Blue Vinyl" in the advertising literature. These grey models are typically fitted with a 5U4 rectifier. In 1966, Supro introduced the black tolex-like covering along with other changes. Both the tube rectified and solid state models featured the sporty white stripe that went around the outside of the cabinet. Thunderbolts began shipping with a solid state (diode bridge) rectifier sometime in mid 1966. The solid state rectifier was likely added to reduce power supply sag and crispen up the amp. The move to a solid state rectifier was accompanied with changes to the baffle board design. These changes were added to address complaints from Bass players who never really liked the amp. The power transformers used in the tube rectified and solid state models are not interchangeable. The power transformer of the solid state rectified model cannot be used as a replacement for the vacuum rectified model. The solid state model transformer lacks the 5.0 Vac winding for the vacuum rectifier heater and the high voltage winding does not have a center tap. Both model types use the same output transformer. All S6420's were fitted with a 15" Jensen Special Design speaker. The speaker was driven by a pair of 6L6GB or 6L6GC power tubes in a cathode biased arrangement. The 5881 power tube can also be used.
In late 1966 or early 1967 the S6420 model was discontinued.
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